1. Field of the Invention
A method and an apparatus for deforming, splitting and chopping of contaminated, or potentially contaminated, heat exchanger tubes into short tubes segments that easily may transported to an off-site location for decontamination, as by abrasive cleaning or other known cleaning steps. The present invention particularly is useful for condenser retubing on nuclear power plants of the boiling water reactor (BWR) type or the pressurized water reactor (PWR) type. Department of Energy regulations governing BWR and PWR reactors require that both exterior and interior surfaces of each removed condenser tube be contamination free, before the tube can be reclaimed as scrap. The present invention has utility for any heat exchanger, or the like, wherein contaminants are transported inside a tube or accumulate outside, on the tube exterior.
2. Brief Description of the Prior Art
Heat exchanger tube bundles used as steam condensers for electric power generating equipment are typically of the indirect type. A large number of parallel tubes carry a liquid, such as water, with at least one stationary tubesheet defining the tubes into a tube bundle. In order to retube, the tube collection must be exposed at one end to provide access to a large number of tube ends, which protrude from a stationary tubesheet. Each tube is tightly pressed into an opening in at least one tubesheet at each end of the collection, in order to form a fluid-tight seal. Water is circulated through the parallel set of tubes while a high temperature gas, typically steam, is circulated about the exterior of the tube bundle.
Prior to the present invention, the need to decontaminate interior wall surfaces of each tube removed from a BWR or PWR condenser tube bundle, for example, has required each tube to be axially pulled from the tubesheets, without being deformed. Therefore, hydraulic tube extractors that grab a tube end and slowly pull out a non-deformed tube typically have been employed at such retubing sites. The prior art technique for removing such contaminated condenser tubes further includes the steps of cutting each contaminated tube into short tubular lengths at the site; packing the cut lengths into a shielded cask at the site; shipping the sealed cask to an off-site facility; and then decontaminating the exterior surfaces of the short tubular lengths by abrasive cleaning, or other cleaning methods. Each short tube length then must be inspected for any residual radiation, before scrap reclamation of that short tube length is permitted. If contamination was found on an interior surface of a short tubular length, further cleaning steps were required.
By contrast, at fossil-fueled electric power plant heat exchanger retubing sites, it has become commonplace to deform each old tube to facilitate a quick removal from the tubesheets. The deformed tubes then simply are fed into a separate device and chopped into lengths short enough for convenient shipping to a scrap dealer. Such tubes are removed by a form of "tube traveler", which comprises two or more pairs of serrated drivers, on parallel axis shafts, so as to define a passageway for axial travel of a deformed tube. The drivers are spaced apart to deformably grip the end of each tube near a tubesheet surface, and then pull, or travel, the tube axially in a deformed condition. Commonly-used tube traveler devices are represented by Cawley, et. al. (U.S. Pat. No. 4,125,928), Harris et al. (U.S. Pat. No. 4,044,444) and Harris (U.S. Pat. No. 4,815,201). Another well-known type of tube traveller is the Tube Walker.TM., manufactured by The Atlantic Group, Inc. of Norfolk, Virginia, assignee of the present invention, and used by its Condenser Services Division.
Therefore, prior to the present invention, the speed and efficiency afforded by a tube traveling step has not been available to remove tubes that potentially are internally contaminated, such as condenser tubes removed from BWR power plants with interior wall surfaces which first must be decontaminated and inspected, before being reclaimed as scrap.
The present invention permits, for the first time, an economical and efficient removal of potentially contaminated heat exchanger tubes. The present invention permits less down time due to quicker tube pulling and chopping steps; more efficient packing of tube segments into a shipping cask; and easier access to interior surfaces of tube segments.